The invention relates to a method of protecting an electronic entity including a microcircuit, in particular a microcircuit card with encrypted access, said protection being aimed more particularly at forms of attack known as “current analysis”. The invention also relates to an electronic entity including a microcircuit, in particular a microcircuit card with encrypted access, equipped with means for obtaining the protection offered by said method.
The person skilled in the art knows that some electronic entities with encrypted access, in particular microcircuit cards, are vulnerable to certain forms of attack based on analyzing certain parameters during a phase of their operation. It is said that information can “leak” from a computation carried out in said electronic entity (the card), typically the execution of a cryptographic protocol instigated by a fraudster in illegal possession of the card. The parameters analyzed during the execution of this kind of protocol can typically be computation time differences or differences in electromagnetic radiation during execution of the computation, but above all are the current consumed by the electronic entity itself during the execution of a cryptographic protocol.
Thus a standard attack consists in having the electronic entity that has fallen into the hands of the fraudster execute a certain number of cryptographic protocols based on random messages, which are therefore bound to fail, but cause the entity (the microcircuit card) to execute each time a cryptographic algorithm, for example the DES (DATA ENCRYPTION STANDARD) algorithm, and analyzing the current consumed during each execution of said DES algorithm. The object of this attack is to discover the secret key of said entity. The DES algorithm is very widely used at present in the field of bank cards, SIM (GSM) cards, pay per view television access cards, and access control cards.
In the case of fraud, i.e. when the fraudster has the card and is seeking to determine the key, the fraudster can connect said card to a reader by means of which he can transmit messages to it and connect it to means for recording the current consumed by the microcircuit during the execution of the operations that it carries out. The fraudster instigates multiple execution of the DES algorithm and the current consumption is detected and memorized each time. From all of this data, and in particular from the current consumption measurements, it is possible to mount attacks whose principle is well known. These SPA-DPA (Simple Power Analysis/Differential Power Analysis) attacks can reconstitute the key of the electronic entity.
In a paper presented on 17 Aug. 2000 at the CHES 2000 conference and published by SPRINGER under the N° 1965, the use of a battery integrated into the electronic entity to supply power to the microcircuit is envisaged. However, the author of the paper finishes by setting aside this solution, deeming it somewhat impractical and difficult to put into practice. The invention solves the problems referred to by the author of this paper.